Evaluation of a MALDI-TOF MS cephalosporinase assay for blood culture isolates

Objectives: Rapid detection of beta-lactamases has the potential to improve antimicrobial stewardship and sepsis outcomes. The aim this study was evaluate a recently TGA-approved cephalosporinase method utilising matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) on blood culture isolates. This compared standard susceptibility testing phenotypic detection. Methods: A total 114 gram negative isolates were retrospectively analysed. Isolates selected either be ceftriaxone non-susceptible by Vitek 2 semi-automated system (version 08.01; bioMerieux, USA, AST-N246 card) (n=31) and/or demonstrate an inducible or ESBL disc approximation (n=32). cohort equal number ceftriaxone-susceptible (n=57). range organisms included Escherichia coli (n=62), followed Serratia marcescens (n=12), Pseudomonas aeruginosa (n=11), Enterobacter cloacae complex (n=10), Klebsiella aerogenes (n=5), pneumoniae (n=3), oxytoca Morganella morganii Acinetobacter calcoaceticus-A. baumannii Citrobacter freundii (n=2). Sub-cultured colonies prepared with MBT STAR-Cepha IVD Kit third-generation cephalosporin hydrolysis detected using STAR-BL Module (Bruker Daltronics) MALDI-TOF MS after 30 min incubation time. Results: assay sensitivity specificity for activity 61.3% 77.1% respectively. 11/11 (100%) producers 5/6 (83.3%) AmpC type producers. Additionally, third generation in 17 26 positive (65.4%) that tested susceptible 2. Of all species included, had lowest concordance results, only 1/11 (9%) MS. Conclusions: Overall lacked cephalosporinases risk false results screening resistance is too high consider its implementation workflow, although there may possible benefit detecting ampC following identification as alternative testing.